116 DR. WILSON ON THE NERVOUS SYSTEM OF THE ASTERID^. 



finely granular, and each with a well-marked nucleus. They lie in a coarsely granular 

 matrix, and have one, sometimes two filaments passing off' from each. 



Some of the filaments run obliquely outwards, while others pass longitudinally along 

 the cord. In Plate XV. fig. 4 we have some of these cells very highly magnified, the 

 fibres from which present the double outline very distinctly. The other branches, before 

 mentioned as passing from these cells, can also be made out in the TIraster : some of 

 these are seen in Plate XIV. fig. 9, passing from the cells upwards by the side of the infe- 

 rior muscle as well as laterally. They, as also the cells, have been coloured with carmine. 

 When more highly magnified, they present a distinct nucleus, deeply coloured, and con- 

 tinuous with the axial cylinder, which is equally tinged (a). The radiating integumentary 

 fibrils already mentioned, as well as their connexion with the cellule-like bodies imme- 

 diately beneath tlie skin, are very weU seen. The nerve-cells extend along the groove as 

 far as the eye-spot ; they become smaller and fewer as they approach the point of the 

 Tay, but above the optic bulb they again increase in number. 



In his Lectures on Comparative Anatomy during the summer of 1857, Professor Goodsir 

 described these cords as " not being mere nerves, but consisting of fine series of ganglionic 

 cords, each cord being beaded or enlarged at the spot where branches pass off." . . . . 

 " They contain a brown pigmental streak extending down their internal surface, are 

 invested by a fine membrane, and consist of delicate filaments, some rimning longitudi- 

 nally, others transversely. They have in addition a gelatinous material, which appears to 

 be cellular." In this description he expressed a view homologous with that held by Miiller. 

 The eye-spot of the Ur aster is large and tolerably pedunculated*. It is connected by 

 means of its peduncle to the root of the tactile organ, from which it projects free. When 

 examined with the ambulacral portion of the ray upwards, it is found to rest partly upon 

 and partly between two calcareous cushions much larger tlian the corresponding ones of 

 the other species f. The spines placed on these masses for protecting the optic bulb, are 

 best examined along with those guarding the tactile organ. 



Like the otlier bulbs, its longitudinal diameter is greater than its transverse. The un- 

 equal distribution of the pigment-cones gives it, in a marked degree, the appearance of 

 being bifid at its free extremity %■ In profile the contour is saddle-shaped, convex trans- 

 versely and concave longitudinally § : this form, however, is only seen when a longi- 

 tudinal section is made through the groove in such a manner as to preserve the calcareous 

 cushion entire ; it is immediately lost as soon as the eye-bulb is removed from its position. 

 The individual cones are very numerous, and so much crowded as to render them diffi- 

 cult to be seen distinctly. When examining them in 1858, I had at first mistaken them 

 for "conical papilla^form projections," and described them as such. Shortly afterwards 

 I succeeded in obtaining a front view of the bulb, and, although still ignorant of its com- 

 pound nature, mentioned its being covered with " irregularly shaped pigment-masses, more 

 or less pointed, and having in the centre a clear space, which, by careful focusing, ap- 

 peared to be pits similar to those seen by Professor Goodsir in Cribella ociilcita"\\. 

 " Tliis pigmented structure seems to me to resemble the compound eye of insects in ar- 



* Plate XV. figs. 3 & 6. t Plate XIV. fig. ]Q.dd. % Plate XV. fig. 6. 



§ Plate XV. fie. 3. II Ibid. fig. 5. 



